Your list of recommended medical tests is about to get longer: the U.S. Preventive Services Task Force says men should get their cholesterol checked regularly after age 35 — women, after 45 — and talk to the doctor about lipid-lowering medication if necessary. At age 40, women should begin getting mammograms every one to two years. (Women with a family history or other breast-cancer risk factors may start earlier.)

The American Cancer Society advises doctors to discuss prostate-cancer screening — although its utility is still being debated by medical experts — with patients at age 50, or younger if they are at high risk for the disease. At 50, men and women should be screened for colorectal cancer. "There's a real need to keep up with vaccinations," says Dr. Jonathan Samet, chair of the department of preventive medicine at the University of Southern California's Keck School of Medicine. That includes tetanus, diphtheria, measles and mumps; the flu vaccine, advisable at all ages, should become a regular part of your preventive routine at 50, according to the CDC.

Weight has a way of sneaking onto the middle-aged frame. "A teaspoon of sugar has 15 calories," says Samet. If you consume an extra teaspoon a day without burning off the calories, a year later, you've gained more than a pound. Ten years later, you've gained 15 pounds. Samet advises vigilance: find a healthy body weight and maintain it with a high-fiber, low-fat, low-sugar diet. Healthy foods should deliver much of your daily requirements of vitamins and minerals. However, many women still don't get enough calcium, which puts them at risk for bone loss, and many Americans are deficient in vitamin D. Your doctor can test you for adequate levels of the vitamin.

Trying to maintain weight and fitness doesn't mean you have to be an Olympic athlete," says Samet. But a daily routine of physical activity gets more and more important as you age — not only to prevent weight gain and chronic illness but also to keep the brain sharp. Studies have shown that even small amounts of moderate exercise can help reduce the risk of dementia. In addition to cardiovascular exercise and strength training, doctors advise working on balance and flexibility, which can help protect against falls and injury in later life.